1. Field of the Invention
This invention relates to pressure measurement apparatus and is more particularly concerned with portable apparatus which may be used external of an inflated article to acquire and display an inflation pressure value from a pressure sensing apparatus located on the article.
2. Description of the Prior Art
The task of checking wheel tire inflation pressures on multi-wheel undercarriages of large aircraft using a conventional pressure gauge connected to a tire inflation valve is a difficult and tiresome task for ground crew. Systems have been proposed which provide for pressure values output by a pressure sensor located on the wheel to be transmitted to the aircraft for display at the flight station in the aircraft cockpit. An advantage of such systems is that they allow tire pressures to be monitored by aircrew at any time during a flight operation, including when the aircraft is taxiing for takeoff and prior to landing. A disadvantage of such systems is their high cost and that tire pressure values can only be read in the cockpit so that when the aircraft is being serviced by groundcrew it is necessary for the aircraft electrical power system to be switched on and for a groundcrew member to enter the cockpit in order to read tire pressure values.
Disclosures of such systems, which display inflation pressure values internally of a vehicle, are to be found, for example in US-A-4845649; US-A-4891973, US-A-4909074; US-A-5140851 and GB-A-2251947.
US-A-4308520 discloses a tire pressure indicator having a wheel mounted pressure transponder unit and a hand-held interrogator unit which can be positioned for coupling with the transponder unit. The transponder unit returns signals to the interrogator unit in accordance with the pressure in the tire mounted on the wheel. When the tire pressure is above a predetermined safe level, a "safe" light on the interrogator is illuminated, and when the pressure is below the safe level a "low" light is illuminated. Thus, this apparatus does not provide a read-out of the tire pressure value.
One aim of the present invention is the provision of portable apparatus, such as may be held in the hand and used to acquire and display an inflation pressure value from pressure sensing apparatus located on an inflated article.
Another aim of this invention is the provision of such a portable apparatus for use in acquiring and displaying an inflation pressure value from pressure sensing apparatus located on a vehicle wheel, e.g. an aircraft undercarriage wheel, without the vehicle power system being switched on or entry having to be made into the vehicle.